The present invention relates to a method of and apparatus for deforming an end portion of a hollow tubular slug which is open at one end and is made of thermoplastic material, threads, rings, grooves or other profiled formations being formed in the outer surface of said end portion.
It is known to produce changes in cross-section in the tubular ends of plastics slugs, in order to form chambers, grooves and threads using multi-part split cores which, for example by axial displacement, are radially adjustable and thus force the tube end which is to be deformed, into the profile of an external mould. In particular where small diameters are concerned, problems arise because the mould components are made up of relatively small, complex and vulnerable parts.
Similar drawbacks also apply to another known method of deforming the ends of plastics slugs by enlarging them with the help of rotating rollers carried on an axially displaceable cone. Where the tube diameters are small, it is difficult to accommodate the mould components; also, the opening up operation takes a long time and this makes it difficult to achieve high production rates.
Also known is a method in which the heated tube end is placed over a mandrel and a wall section of the tube is upset by means of an axially displaceable tool, the plastics material which is being deformed being forced at the upsetting location into a mould cavity so that it forms a fold. A particular disadvantage of this method is that, where the wall thickness is small in comparison to the diameter, the fold cannot be produced with any accuracy. Frequently, additional folds appear at the upsetting location, and these detract from the appearance of the finished article.
Further, it is known to enlarge the end of a tube held in an external mould, by using an axially displaceable mandrel which enlarges the tube end from the end face, producing the desired cross-sectional shape. In this context, however, accurate cross-sectional shapes cannot be produced. Again, the versatility of the moulds is limited because the mandrel cannot contain any undercuts.
In addition, it is known to insert an annular body of elastically deformable material into the tube end, and, by axial compression or radial enlargement of the annular body, to provide the tube wall with grooves or the like. This method, too, does not of itself satisfy all the requirements of industrial production in terms of rapid and accurate changing of cross-section.
An object of the invention, therefore, is to create a simple method and apparatus, in particular for application to small diameter tubes, by which one can rapidly and accurately modify the cross-section of a tubular end portion of a thermoplastic hollow slug which has been preheated to a readily deformable state, without at the same time incurring a high scrap rate.